Mucociliary clearance of inhaled particles from the tracheobronchial tree is an important defense mechanism of the lungs. Circumstantial evidence indicates that airway secretion of ions, water and mucus is an important factor in determining the rate of mucociliary clearance. Since the normal and abnormal physiology of these secretory processes is only partially known, my proposal is to study the interrelationships of these processes. Previously, we have shown there is a predominant chloride pump directed toward the tracheal lumen and a sodium pump facing in the opposite direction. We performed the initial studies supported by this grant to further characterise this ion transport across dog tracheal epithelium. These studies showed that there is an interdependent movement of Cl- and Na ion toward the tracheal lumen which required both Cl- and Na ion in the bathing media. Stimulation of ion transport by acetylcholine and terbutaline and inhibition of transport by furosemide required the presence of Cl- and Na ion. Addiitonally, we studied the effects of calcium concentration in the bathing media on the electrical and ion transport properties of dog tracheal epithelium. These studies showed that lack of calcium decreased transepithelial electrical resistance. Furthermore, calcium was necessary for the full electrical response to histamine but was not necessary for responses to acetylcholine or terbutaline. We have also developed an in vitro technique for characterizing the kinetics of sulfated mucous glycoprotein secretion in dog tracheal epithelium. We showed that lack of calcium decreased both secretion rate and the pool size of sulfated mucous glycoproteins in dog tracheal epithelium. Also, we showed that the turnover time of the pool is independent of calcium concentration in the bathing media.